also use natural cracks in the ice to feed and, in
the case of minke whales, to breathe.
That the great, shifting expanses of ice
around us, utterly devoid of soil and rooted
plants, support any life at all - let alone in such
profusion-seems impossible. Andre Belem, a
graduate student from the University of Rio
Grande in Brazil, offers me a dramatic insight
when he shows me a test tube in which he has
melted a small chunk of sea ice. "Look," he
says in amazement. A thick yellowish sludge of
algae floats in the bottom. "There's more life
in there than in the water of an estuary."
Indeed algal concentrations in the sea ice are
among the highest ever recorded in any ocean.
As the ice grows, the crystals snag algae.
Channels winding among the crystals bring
seawater - and nutrients -to the algae, which
lure krill and krill larvae to the bottom of the
ice floes, where they graze like tiny cows.
ONE DAY during our last week I climb
with Jim Cooper, the electronics
technician, to the top of the science
mast, 130 feet above the ice. As he
rubs the frost off the satellite receivers and
meteorological sensors, I look down at a quilt
of ice floes spreading to the horizon under the
clear blue sky. Smoky wisps curl up around
the ship like genies-ice crystals forming as
water vapor from the lead we're gliding
through encounters the colder air.
This transfer of heat from water to air is
expressive of a much grander redistribution
triggered by the sea ice: the streaming of cold
water from the Antarctic toward the Equator.
As seawater around Antarctica freezes, it
squeezes out cold, dense brine, some of which
sinks to deeper water then moves north. It
eventually mixes with warmer water, rises,
and begins flowing back toward Antarctica.
National Geographic, May 1996